Synergistic antitumor effect of combined paclitaxel with FEN1 inhibitor in cervical cancer cells

Construction of single-molecule counting-based biosensors for DNA-modifying enzymes: A review

DNA-modifying enzymes act as critical regulators in a wide range of genetic functions (e.g., DNA damage & repair, DNA replication), and their aberrant expression may interfere with regular genetic functions and induce various malignant diseases including cancers. DNA-modifying enzymes have emerged as the potential biomarkers in early diagnosis of diseases and new therapeutic targets in genomic research. Consequently, the development of highly specific and sensitive biosensors for the detection of DNA-modifying enzymes is of great importance for basic biomedical research, disease diagnosis, and drug discovery. Single-molecule fluorescence detection has been widely implemented in the field of molecular diagnosis due to its simplicity, high sensitivity, visualization capability, and low sample consumption. In this paper, we summarize the recent advances in single-molecule counting-based biosensors for DNA-modifying enzyme (i.e, alkaline phosphatase, DNA methyltransferase, DNA glycosylase, flap endonuclease 1, and telomerase) assays in the past four years (2019 - 2023). We highlight the principles and applications of these biosensors, and give new insight into the future challenges and perspectives in the development of single-molecule counting-based biosensors.

FEN1 promotes cancer progression of cholangiocarcinoma by regulating the Wnt/β-catenin signaling pathway

PURPOSE

Cholangiocarcinoma (CHOL) comprises a cluster of highly heterogeneous malignant biliary tumors. Flap endonuclease-1 (FEN1) is a member of the Rad2 structure-specific nuclease family. This study aimed to explore the biological functions and mechanisms of FEN1 in CHOL.

METHODS

FEN1 expression was analyzed in tissues of patients with CHOL and FEN1 mutations. We observe the influence of FEN1 on cellular proliferation, migration, and invasion, as well as on DNA damage repair and glycolysis. Western blotting was performed to determine the regulatory mechanism of FEN1 in CHOL progression.

RESULTS

FEN1 was highly expressed in the cancer tissues of CHOL patients. The high mutation rate of FEN1 in CHOL tissues was mainly due to the amplified repeats. FEN1 promotes the proliferation, migration, and invasion of HUCCT1 and QBC939 cells. In addition, FEN1 induced DNA damage repair and aerobic glycolysis in CHOL cells. FEN1 also promoted xenograft tumor growth in vivo. Moreover, we showed that FEN1 mediated the epithelial-mesenchymal transition (EMT) of CHOL. FEN1-mediated EMT was found to be transduced by the Wnt/β-catenin signaling pathway.

CONCLUSION

FEN1 was significantly overexpressed in CHOL tissues, and FEN1 regulates the progression of CHOL through the Wnt/β-catenin signaling pathway.

Lappaconitine sulfate inhibits proliferation and induces mitochondrial-mediated apoptosis via regulating PI3K/AKT/GSK3β signaling pathway in HeLa cells

Lappaconitine (LA), a diterpenoid alkaloid extracted from the root of Aconitum sinomontanum Nakai, exhibits broad pharmacological effects, including anti-tumor activity. The inhibitory effect of lappaconitine hydrochloride (LH) on HepG2 and HCT-116 cells and the toxicity of lappaconitine sulfate (LS) on HT-29, A549, and HepG2 cells have been described. But the mechanisms of LA against human cervical cancer HeLa cells still need to be clarified. This study was designed to investigate the effects and molecular mechanisms of lappaconitine sulfate (LS) on the growth inhibition and apoptosis in HeLa cells. The cell viability and proliferation were evaluated using the Cell Counting Kit-8 (CCK-8) and 5-ethynyl-2´-deoxyuridine (EdU) assay, respectively. The cell cycle distribution and apoptosis were detected by flow cytometry analysis and 4', 6-diamidino-2-phenylindole (DAPI) staining. The mitochondrial membrane potential (MMP) was determined through the 5, 5', 6, 6'-tetrachloro-1, 1', 3, 3'-tetraethylbenzimi-dazolyl carbocyanine iodide (JC-1) staining. The cell cycle arrest-, apoptosis-, and the phosphatidylinositol-3-kinase/protein kinase B/glycogen synthase kinase 3β (PI3K/AKT/GSK3β) pathway-related proteins were estimated by western blot analysis. LS markedly reduced the viability and suppressed the proliferation of HeLa cells. LS induced G0/G1 cell cycle arrest through the inhibition of Cyclin D1, p-Rb, and induction of p21 and p53. Furthermore, LS triggered apoptosis through the activation of mitochondrial-mediated pathway based on decrease of Bcl-2/Bax ratio and MMP and activation of caspase-9/7/3. Additionally, LS led to constitutive downregulation of the PI3K/AKT/GSK3β signaling pathway. Collectively, LS inhibited cell proliferation and induced apoptosis through mitochondrial-mediated pathway by suppression of the PI3K/AKT/GSK3β signaling pathway in HeLa cells.

A one-pot transcriptional assay method that detects the tumor biomarker FEN1 based on its flap cleavage activity

BACKGROUND

Detection of tumor biomarkers in body fluids is a significant advancement in cancer treatment because it allows diagnosis without invasive tissue biopsies. Nucleases have long been regarded as a potential class of biomarkers that can indicate the occurrence and progression of cancers. Among these, flap endonuclease 1 (FEN1) plays an important role in DNA replication and repair, and also overexpressed in abnormally proliferating cells such as cancer cells. FEN1 is thus considered to be a potential biomarker as well as a target for cancer therapy.

RESULTS

We developed a novel method for detecting FEN1 based on its specific endonuclease activity which incises bifurcated nucleic acids (flaps), in combination with in vitro transcription. Developed method uses a simple DNA structure (substrate DNA) carrying a short 5'-flap sequence, and a single-stranded sensor DNA encoding the Broccoli light-up aptamer. When the assay mixture was supplied with a FEN1-containing sample, the flap sequence encoding the sense sequence of T7 promoter was cleaved and released from the substrate DNA. Because the sensor DNA was designed to carry the Broccoli RNA aptamer under the antisense sequence of T7 promoter, hybridization of the excised flap onto the sensor DNA initiated the transcription of the Broccoli RNA aptamer, enabling determination of the FEN1 titer based on the fluorescence of transcribed Broccoli aptamer. By using a combination of FEN1-mediated generation of a short oligonucleotide and subsequent oligonucleotide-dependent in vitro transcription, this method could detect FEN1 in biological samples within 1 h.

SIGNIFICANCE AND NOVELTY

Developed method enables the detection of FEN1 by a simple one-pot reaction. It can detect sub-nanomolar concentrations of FEN1 within an hour, and has the potential to be used for cancer diagnosis, prognosis, and drug screening. It also enables easy identification of compounds that inhibit FEN1 activity and is thus a versatile platform for screening anti-cancer drugs. We anticipate that the basic principles of this assay can be applied to detect other biomolecules, such as nucleic acids.

FEN1 inhibitor SC13 promotes CAR-T cells infiltration into solid tumours through cGAS-STING signalling pathway

It is well known that chimeric antigen receptor T-cell immunotherapy (CAR-T-cell immunotherapy) has excellent therapeutic effect in haematological tumours, but it still faces great challenges in solid tumours, including inefficient T-cell tumour infiltration and poor functional persistence. Flap structure-specific endonuclease 1 (FEN1), highly expressed in a variety of cancer cells, plays an important role in both DNA replication and repair. Previous studies have reported that FEN1 inhibition is an effective strategy for cancer treatment. Therefore, we hypothesized whether FEN1 inhibitors combined with CAR-T-cell immunotherapy would have a stronger killing effect on solid tumours. The results showed that low dose of FEN1 inhibitors SC13 could induce an increase of double-stranded broken DNA (dsDNA) in the cytoplasm. Cytosolic dsDNA can activate the cyclic GMP-AMP synthase-stimulator of interferon gene signalling pathway and increase the secretion of chemokines. In vivo, under the action of FEN1 inhibitor SC13, more chemokines were produced at solid tumour sites, which promoted the infiltration of CAR-T cells and improved anti-tumour immunity. These findings suggest that FEN1 inhibitors could enable CAR-T cells to overcome poor T-cell infiltration and improve the treatment of solid tumours.

Distinctive Formation of a DNA-Protein Cross-Link during the Repair of DNA Oxidative Damage: Insights into Human Disease from MD Simulations and QM/MM Calculations

Reactive oxygen species damage DNA and result in health issues. The major damage product, 8-oxo-7,8-dihydroguanine (8oG), is repaired by human adenine DNA glycosylase homologue (MUTYH). Although MUTYH misfunction is associated with a genetic disorder called MUTYH-associated polyposis (MAP) and MUTYH is a potential target for cancer drugs, the catalytic mechanism required to develop disease treatments is debated in the literature. This study uses molecular dynamics simulations and quantum mechanics/molecular mechanics techniques initiated from DNA-protein complexes that represent different stages of the repair pathway to map the catalytic mechanism of the wild-type MUTYH bacterial homologue (MutY). This multipronged computational approach characterizes a DNA-protein cross-linking mechanism that is consistent with all previous experimental data and is a distinct pathway across the broad class of monofunctional glycosylase repair enzymes. In addition to clarifying how the cross-link is formed, accommodated by the enzyme, and hydrolyzed for product release, our calculations rationalize why cross-link formation is favored over immediate glycosidic bond hydrolysis, the accepted mechanism for all other monofunctional DNA glycosylases to date. Calculations on the Y126F mutant MutY highlight critical roles for active site residues throughout the reaction, while investigation of the N146S mutant rationalizes the connection between the analogous N224S MUTYH mutation and MAP. In addition to furthering our knowledge of the chemistry associated with a devastating disorder, the structural information gained about the distinctive MutY mechanism compared to other repair enzymes represents an important step for the development of specific and potent small-molecule inhibitors as cancer therapeutics.

Small-Molecule Inhibitors Targeting FEN1 for Cancer Therapy

DNA damage repair plays a key role in maintaining genomic stability and integrity. Flap endonuclease 1 (FEN1) is a core protein in the base excision repair (BER) pathway and participates in Okazaki fragment maturation during DNA replication. Several studies have implicated FEN1 in the regulation of other DNA repair pathways, including homologous recombination repair (HRR) and non-homologous end joining (NHEJ). Abnormal expression or mutation of FEN1 in cells can cause a series of pathological responses, leading to various diseases, including cancers. Moreover, overexpression of FEN1 contributes to drug resistance in several types of cancers. All this supports the hypothesis that FEN1 could be a therapeutic target for cancer treatment. Targeting FEN1 has been verified as an effective strategy in mono or combined treatment of cancer. Small-molecule compounds targeting FEN1 have also been developed and detected in cancer regression. In this review, we summarize the recent development of small-molecule inhibitors targeting FEN1 in recent years, thereby expanding their therapeutic potential and application.

Observation of the cervical microbiome in the progression of cervical intraepithelial neoplasia

OBJECTIVE

Cervical microbial community in the cervical intraepithelial neoplasia and cervical cancer patients was analysed to study its composition, diversity and signalling pathways by high-throughput 16S rDNA sequencing,and the candidate genes associated with occurrence and progression of cervical intraepithelial neoplasia were screened out and the model was established to predict the evolution of cervical intraepithelial neoplasia malignant transformation from the cervical microbial genes aspect.

METHODS

Cervical tissues of normal, cervical intraepithelial neoplasia and cervical cancer patients without receiving any treatment were collected. The correlation between candidate genes and cervical intraepithelial neoplasia progression was initially determined by analyzing the microbial flora. Real-time fluorescence quantitative PCR was used to detect the expression of candidate genes in different cervical tissues, ROC curve and logistic regression was used to analyse and predict the risk factors related to the occurrence and progression of cervical intraepithelial neoplasia. Finally, the early warning model of cervical intraepithelial neoplasia occurrence and progression is established.

RESULTS

Cervical tissues from normal, cervical intraepithelial neoplasia and cervical cancer patients were collected for microbial community high-throughput 16S rDNA sequencing. The analysis revealed five different pathways related to cervical intraepithelial neoplasia. 10 candidate genes were selected by further bioinformatics analysis and preliminary screening. Real time PCR, ROC curve and Logistic regression analysis showed that human papillomavirus infection, TCT severity, ABCG2, TDG, PCNA were independent risk factors for cervical intraepithelial neoplasia. We used these indicators to establish a random forest model. Seven models were built through different combinations. The model 4 (ABCG2 + PCNA + TDG) was the best early warning model for the occurrence and progression of CIN.

CONCLUSIONS

A total of 5 differential pathways and 10 candidate genes related to occurrence and progression of cervical intraepithelial neoplasia were found in cervical microbial community. This study firstly identified the genes from cervical microbial community that play an important role in the occurrence and progression of cervical intraepithelial neoplasia. At the same time, the early warning model including ABCG2 + PCNA+TDG genes provided a new idea and target for clinical prediction and blocking the evolution of cervical intraepithelial neoplasia malignant transformation from the aspect of cervical microbiological related genes.

Downregulation of MEIS1 mediated by ELFN1-AS1/EZH2/DNMT3a axis promotes tumorigenesis and oxaliplatin resistance in colorectal cancer

Oxaliplatin is widely used in the frontline treatment of colorectal cancer (CRC), but an estimated 50% of patients will eventually stop responding to treatment due to acquired resistance. This study revealed that diminished MEIS1 expression was detected in CRC and harmed the survival of CRC patients. MEIS1 impaired CRC cell viabilities and tumor growth in mice and enhanced CRC cell sensitivity to oxaliplatin by preventing DNA damage repair. Mechanistically, oxaliplatin resistance following MEIS1 suppression was critically dependent on enhanced FEN1 expression. Subsequently, we confirmed that EZH2-DNMT3a was assisted by lncRNA ELFN1-AS1 in locating the promoter of MEIS1 to suppress MEIS1 transcription epigenetically. Based on the above, therapeutics targeting the role of MEIS1 in oxaliplatin resistance were developed and our results suggested that the combination of oxaliplatin with either ELFN1-AS1 ASO or EZH2 inhibitor GSK126 could largely suppress tumor growth and reverse oxaliplatin resistance. This study highlights the potential of therapeutics targeting ELFN1-AS1 and EZH2 in cell survival and oxaliplatin resistance, based on their controlling of MEIS1 expression, which deserve further verification as a prospective therapeutic strategy.

circ_ZFR Is Linked to Paclitaxel Resistance in Cervical Cancer via miR-944 Sponging and IL-10 Upregulation

Objective

Cervical cancer (CC) has an elevated rate of invasion and death despite surgical treatment, radiotherapy, and chemotherapy. Several studies revealed that circRNAs have a key contribution to the resistance of drugs against different types of carcinomas. The goal of the existing study was to figure out what role circ_ZFR plays in paclitaxel (PTX) resistance in cervical cancer (CC) patients.

Materials and Methods

Herein, two types of CC cells (SiHa/PTX and Hela/PTX) were utilized. The levels of IL-10 mRNA, miR-944, and circ_ZFR were measured using qRT-PCR analyses. The CCK-8 assay was used to determine PTX resistance. The IL-10 expression was measured via the ELISA technique. The combination of miR-944 and circ_ZFR or IL-10 was validated using a dual-luciferase reporter (DLR) assay.

Results

The amount of circ_ZFR was increased in PTX-resistant CC cells and tissues. In PTX-resistant CC cells, knocking down circ_ZFR expression decreased PTX resistance. circ_ZFR knockdown significantly reduced IL-10 expression via sponging miR-944, increasing PTX sensitivity in PTX-resistant CC cells.

Conclusion

circ_ZFR knockdown has a considerable role in overwhelming CC-associated PTX resistance by modifying the axis of miR-944/IL-10 axis, suggesting that developing a circRNA target-based treatment could be considered prevent CC progression.

Significance of base excision repair to human health

Oxidative and alkylating DNA damage occurs under normal physiological conditions and exogenous exposure to DNA damaging agents. To counteract DNA base damage, cells have evolved several defense mechanisms that act at different levels to prevent or repair DNA base damage. Cells combat genomic lesions like these including base modifications, abasic sites, as well as single-strand breaks, via the base excision repair (BER) pathway. In general, the core BER process involves well-coordinated five-step reactions to correct DNA base damage. In this review, we will uncover the current understanding of BER mechanisms to maintain genomic stability and the biological consequences of its failure due to repair gene mutations. The malfunction of BER can often lead to BER intermediate accumulation, which is genotoxic and can lead to different types of human disease. Finally, we will address the use of BER intermediates for targeted cancer therapy.

Dual-Mode FEN1 Activity Detection Based on Nt.BstNBI-Induced Tandem Signal Amplification

Flap endonuclease 1 (FEN1) is a structure-specific nuclease that cleaves the 5' single-stranded protrusion (also known as 5' flap) during Okazaki fragment processing. It is overexpressed in various types of human cancer cells and has been considered as an important biomarker for cancer diagnosis. However, conventional methods for FEN1 assay usually suffer from complicated platform and laborious procedures with a limited sensitivity. Here, we developed a dual-signal method for sensitive detection of FEN1 on the basis of duplex-specific nuclease actuated cyclic enzymatic repairing-mediated signal amplification. Once the 5' flap of the double-flap DNA substrate was cleaved by target FEN1, the cleaved 5' flap initiated strand-displacement amplification to produce plenty of G-rich DNA (G) sequences. These G sequences that self-assembled into G-quadruplexes in the presence of hemin revealed horseradish-peroxidase-like catalytic activities as well as fluorescence enhancement of thioflavin T. The UV-vis signal showed a good linear relationship with the logarithm of FEN1 activity ranging from 0.03 to 1.5 U with a detection limit of 0.01 U. The fluorescence signal correlated linearly with the logarithm of FEN1 activity ranging from 0.001 to 1.5 U with a detection limit of 0.75 mU. In addition, FEN1 can be visualized not only by colorimetry but also by fluorescence (under ice-water mixture conditions). This reliable, accurate, and convenient method would be a potential powerful tool in point-of-care testing applications and therapeutic response assessment.

Small Molecule Inhibitors Targeting Key Proteins in the DNA Damage Response for Cancer Therapy

DNA damage response (DDR) is a complicated interactional pathway. Defects that occur in subordinate pathways of the DDR pathway can lead to genomic instability and cancer susceptibility. Abnormal expression of some proteins in DDR, especially in the DNA repair pathway, are associated with the subsistence and resistance of cancer cells. Therefore, the development of small molecule inhibitors targeting the chief proteins in the DDR pathway is an effective strategy for cancer therapy. In this review, we summarize the development of small molecule inhibitors targeting chief proteins in the DDR pathway, particularly focusing on their implications for cancer therapy. We present the action mode of DDR molecule inhibitors in preclinical studies and clinical cancer therapy, including monotherapy and combination therapy with chemotherapeutic drugs or checkpoint suppression therapy.

Signal-Amplified Detection of the Tumor Biomarker FEN1 Based on Cleavage-Induced Ligation of a Dumbbell DNA Probe and Rolling Circle Amplification

Flap endonuclease 1 (FEN1), an endogenous nuclease with the ability to cleave the 5' overhang of branched dsDNA, is of significance in DNA replication and repair. The overexpression of FEN1 is common in cancer because of the ubiquitous upregulation of DNA replication; thus, FEN1 has been recognized as a potential biomarker in oncological investigations. However, few analytical methods targeting FEN1 with high sensitivity and simplicity have been developed. This work developed a signal-amplified detection of FEN1 based on the cleavage-induced ligation of a dumbbell DNA probe and rolling circle amplification (RCA). A flapped dumbbell DNA probe (FDP) was rationally designed with a FEN1 cleavable flap at the 5' end. The cleavage generated a nick site with juxtaposed 5' phosphate and 3' hydroxyl ends, which were linkable by T4 DNA ligase to form a closed dumbbell DNA probe (CDP) with a circular conformation. The CDP functioned as a template for RCA, which produced abundant DNA that could be probed using SYBR Green I. The highly sensitive detection of FEN1 with a limit of detection of 15 fM was achieved, and this method showed high specificity, which enabled the quantification of FEN1 in real samples. The inhibitory effects of chemicals on FEN1 were also evaluated. This study represents the first attempt to develop an FEN1 assay that involves signal amplification, and the novel biosensor method enriches the tools for FEN1-based diagnostics.

FEN1 is a prognostic biomarker for ER+ breast cancer and associated with tamoxifen resistance through the ERα/cyclin D1/Rb axis

Background

Tamoxifen is an important choice in endocrine therapy for patients with oestrogen receptor-positive (ER+) breast cancer, and disease progression-associated resistance to tamoxifen therapy is still challenging. Flap endonuclease-1 (FEN1) is used as a prognostic biomarker and is considered to participate in proliferation, migration, and drug resistance in multiple cancers, especially breast cancer, but the prognostic function of FEN1 in ER+ breast cancer, and whether FEN1 is related to tamoxifen resistance or not, remain to be explored.

Methods

On-line database Kaplan-Meier (KM) plotter, GEO datasets, and immunohistochemistry were used to analyse the prognostic value of FEN1 in ER+ breast cancer from mRNA and protein levels. Cell viability assay and colony formation assays showed the response of tamoxifen in MCF-7 and T47D cells. Microarray data with FEN1 siRNA versus control group in MCF-7 cells were analysed by Gene Set Enrichment Analysis (GSEA). The protein levels downstream of FEN1 were detected by western blot assay.

Results

ER+ breast cancer patients who received tamoxifen for adjuvant endocrine therapy with poor prognosis showed a high expression of FEN1. MCF-7 and T47D appeared resistant to tamoxifen after FEN1 over-expression and increased sensitivity to tamoxifen after FEN1 knockdown. Importantly, FEN1 over-expression could activate tamoxifen resistance through the ERα/cyclin D1/Rb axis.

Conclusions

As a biomarker of tamoxifen effectiveness, FEN1 participates in tamoxifen resistance through ERα/cyclin D1/Rb axis. In the future, reversing tamoxifen resistance by knocking-down FEN1 or by way of action as a small molecular inhibitor of FEN1 warrants further investigation.

FEN1 inhibitor synergizes with low-dose camptothecin to induce increased cell killing via the mitochondria mediated apoptotic pathway

Camptothecin has been used in tumor therapy for a long time but its antitumor effect is rather limited due to the side effect and the drug resistance. FEN1, a major component of DNA repair systems, plays important roles in maintaining genomic stability via DNA replication and repair. Here we found that FEN1 inhibitor greatly sensitizes cancer cells to low-dose camptothecin. The combinative treatment of FEN1 inhibitor and 1 nM camptothecin induced a synthetic lethal effect, which synergistically suppressed cancer cell proliferation and significantly mediated apoptosis both in vitro and in vivo. Our study suggested that targeting FEN1 could be a potent strategy for tumor-targeting cancer therapy.

The inhibition of colorectal cancer growth by the natural product macrocarpal I

BACKGROUND

Presently, few small molecule compounds are used as targeted therapy drugs in the treatment of colorectal cancer (CRC). It is important to identify new small molecule compounds, which can be used in the treatment of CRC.

METHODS

In this study, we selected four protein molecules as drug targets: PRL-3 (Phosphatase of regenerating liver 3), CLIC4 (Chloride intracellular channel 4), THBS2 (Thrombospondin 2), and BGN (Biglycan). These protein molecules were associated with the growth and metastasis of CRC cells. Small molecular compounds were screened on the basis of their target structures. Thus, five small molecule compounds were screened from each target structure, and three small molecule compounds (macrocarpal I, sildenafil, and neoandrographolide) were found to bind with two drug targets at the same time. Further experiments revealed that the inhibition rate of macrocarpal I was the highest in CRC cells. Therefore, we determined the effects of macrocarpal I on proliferation, apoptosis, cytoskeleton of CRC cells, and subcutaneous tumorigenesis in nude mice. Furthermore, RNA-seq analysis was performed to determine the molecular mechanism through which macrocarpal I inhibited the progression of CRC.

RESULTS

We found that macrocarpal I could effectively inhibit proliferation, colony formation of CRC cells, and subcutaneous tumorigenesis in nude mice. Moreover, it also destroyed the cytoskeleton of CRC cells and promoted apoptosis. The effects on kinase activity, cytoskeleton, and DNA repair is the mechanism of macrocarpal I to inhibiting CRC growth.

CONCLUSION

Macrocarpal I is a small molecule compound that can effectively inhibit the progression of CRC. Thus, macrocarpal I is a therapeutic compound that shows promising results in the treatment of advanced CRC.

Biological and clinical significance of flap endonuclease‑1 in triple‑negative breast cancer: Support of metastasis and a poor prognosis

Flap endonuclease‑1 (FEN1), a structure‑specific nuclease participating in DNA replication and repair processes, has been confirmed to promote the proliferation and drug resistance of tumor cells. However, the biological functions of FEN1 in cancer cell migration and invasion have not been defined. In the present study, using online database analysis and immunohistochemistry of the specimens, it was found that FEN1 expression was associated with a highly invasive triple‑negative breast cancer (TNBC) subtype in both breast cancer samples from the Oncomine database and from patients recruited into the study. Furthermore, FEN1 was an important biomarker of lymph node metastasis and poor prognosis in patients with TNBC. FEN1 promoted migration of TNBC cell lines and FEN1 knockdown reduced the number of spontaneous lung metastasis in vivo. Ingenuity Pathway Analysis of FEN1‑related transcripts in 198 patients with TNBC demonstrated that the polo‑like kinase family may be the downstream target of FEN1. PLK4 was further identified as a critical target of FEN1 mediating TNBC cell migration, by regulating actin cytoskeleton rearrangement. The results of the present study validate FEN1 as a therapeutic target in patients with TNBC and revealed a new role for FEN1 in regulating TNBC invasion and metastasis.

Transcriptome Analysis of FEN1 Knockdown HEK293T Cell Strain Reveals Alteration in Nucleic Acid Metabolism, Virus Infection, Cell Morphogenesis and Cancer Development

AIM AND OBJECTIVE

Flap endonuclease-1 (FEN1) plays a central role in DNA replication and DNA damage repair process. In mammals, FEN1 functional sites variation is related to cancer and chronic inflammation, and supports the role of FEN1 as a tumor suppressor. However, FEN1 is overexpressed in multiple types of cancer cells and is associated with drug resistance, supporting its role as an oncogene. Hence, it is vital to explore the multi-functions of FEN1 in normal cell metabolic process. This study was undertaken to examine how the gene expression profile changes when FEN1 is downregulated in 293T cells.

MATERIALS AND METHODS

Using the RNA sequencing and real-time PCR approaches, the transcript expression profile of FEN1 knockdown HEK293T cells have been detected for the next step evaluation, analyzation, and validation.

RESULTS

Our results confirmed that FEN1 is important for cell viability. We showed that when FEN1 downregulation led to the interruption of nucleic acids related metabolisms, cell cycle related metabolisms are significantly interrupted. FEN1 may also participate in non-coding RNA processing, ribosome RNA processing, transfer RNA processing, ribosome biogenesis, virus infection and cell morphogenesis.

CONCLUSION

These findings provide insight into how FEN1 nuclease might regulate a wide variety of biological processes, and laid the foundation for understanding the role of other RAD2 family nucleases in cell growth and metabolism.

Jianpi-yangwei decoction inhibits DNA damage repair in the drug resistance of gastric cancer by reducing FEN1 expression

Background

Flap Endonuclease 1(FEN1) has been considered as a new tumor marker in recent years and Jianpi Yangwei Decoction (JPYW) is a basic Traditional Chinese Medicine (TCM) for the treatment of gastric cancer. This study aimed to explore the role of FEN1-mediated DNA damage repair in the drug resistance of gastric cancer and the effect of JPYW on it by employing BGC823/5-Fu drug-resistant cell model.

Methods

The DNA repair efficiency of BGC823 and BGC823/5-Fu was compared intracellularly and extracellularly using an extrachromosomal assay system and the reconstituted base excision repair assay. By comparing gene and protein expression and identifying cell survival rates after knockdown or high expression of FEN1, the correlation between FEN1 high expression and 5-Fluorouracil (5-Fu) drug resistance was revealed. The effect of JPYW on DNA damage repair and FEN1 expression was observed by the degree of γ-H2AX phosphorylation in the cells, DNA repair efficiency and enzyme activity, et al.

Results

BGC823/5-Fu had a higher DNA repair efficiency than BGC823(P < 0.001), which proved to be both intracellular and extracellular. FEN1 was highly expressed in BGC823/5-Fu regardless of gene level(P < 0.001) or protein level. Furthermore, manipulating FEN1 altered the sensitivity of cancer cells to chemotherapeutic drug 5-Fu. Different concentrations of JPYW were used to investigate the inhibitory effect on the expression of FEN1 and DNA damage repair. JPYW inhibited DNA damage repair both intracellularly and extracellularly: the phosphorylation of γ-H2AX increased, with more DNA damage in the cells; the synthetic 8-oxo dG damage repair was reduced; and the ability of cell lysates to repair DNA damage decreased. The decrease of FEN1 expression in BGC823/5-Fu had a concentration dependent relationship with JYPW. In addition, JPYW inhibited the activity of FEN1 at the enzymatic level, as the amount of cut-off synthetic ³²p labeled DNA substrates were decreased.

Conclusion

FEN1 was highly expressed in drug-resistance gastric cancer cells BGC823/5-Fu, which leading to BGC823 resistant to (5-Fu) by acting on DNA damage repair. JPYW inhibited DNA damage repair and reversed 5-Fu drug resistance by reducing FEN1 expression and inhibiting FEN1 functional activity.

Inhibition of FEN1 Increases Arsenic Trioxide-Induced ROS Accumulation and Cell Death: Novel Therapeutic Potential for Triple Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer, which is very difficult to treat and commonly develops resistance to chemotherapy. The following study investigated whether the inhibition of Flap Endonuclease 1 (FEN1) expression, the key enzyme in the base excision repair (BER) pathway, could improve the anti-tumor effect of arsenic trioxide (ATO), which is a reactive oxygen species (ROS) inducer. Our data showed that ATO could increase the expression of FEN1, and the knockdown of FEN1 could significantly enhance the sensitivity of TNBC cells to ATO both in vitro and in vivo. Further mechanism studies revealed that silencing FEN1 in combination with low doses of ATO might increase intracellular ROS and reduce glutathione (GSH) levels, by reducing the nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2); elevating ROS leaded to apoptosis and p38 and JNK pathway activating. In conclusion, our study suggested the combination of FEN1 knockdown and ATO could induce TNBC cell death by promoting ROS production. FEN1 knockdown can effectively decrease the application concentrations of ATO, thus providing a possibility for the treatment of TNBC with ATO.

Upregulation of FEN1 Is Associated with the Tumor Progression and Prognosis of Hepatocellular Carcinoma

Background

Studies show that patients with hepatocellular carcinoma (HCC) have poor prognosis, particularly when patients are diagnosed at late stages of the disease development. The flap endonuclease 1 (FEN1) gene is overexpressed in multiple malignant tumors and may promote tumor aggressiveness. However, its expression profile and functional roles in HCC are still unclear. Here, we evaluated the molecular mechanisms of FEN1 in HCC.

Methods

The expression of FEN1 in HCC was evaluated using HCC mRNA expression data from TCGA and GEO databases. The expression of FEN1 was also confirmed by immunohistochemistry (IHC) using a tissue microarray (TMA) cohort with a total of 396 HCC patients. Kaplan-Meier analysis and univariate and multivariate Cox regression analyses were used to determine the correlation between FEN1 expression and survival rate of HCC patients. The molecular mechanism and biological functions of FEN1 in HCC were predicted using functional and pathway enrichment analysis in vitro experiments.

Results

FEN1 was overexpressed in multiple HCC cohorts at both mRNA and protein levels. The receiver operating characteristic (ROC) curve showed that FEN1 can serve as a diagnostic predictor of HCC. Meanwhile, patients with high FEN1 expression levels showed lower overall survival (OS) and relapse-free survival (RFS) rates than those with low FEN1 expression. More importantly, we found that FEN1 elevation was an independent prognostic factor for OS and RFS in HCC patients based on univariate and multivariate analyses, indicating that FEN1 might be a potential prognostic marker in HCC. Furthermore, knocking down FEN1 resulted in suppressed cell proliferation and migration in vitro. This could have been due to regulation expressions of c-Myc, survivin, and cyclin D1 genes, indicating that FEN1 may function as an oncogene through its role in the cell cycle and DNA replication pathway.

Conclusion

Our study indicated that high FEN1 expression might function as a biomarker for diagnosis and prognosis. In addition, the study confirms that FEN1 is an oncogene in HCC progression.

FEN1 inhibitor increases sensitivity of radiotherapy in cervical cancer cells

Background

Cervical cancer is one of the most common causes of cancer‐associated mortality among affected women in the world. At present, treatment with weekly cisplatin plus ionizing radiation (IR) therapy is the standard regimen for cervical cancer, especially for locally advanced cervical cancer. The purpose of this study is to determine whether FEN1 inhibitors could enhance the therapeutic effect of IR therapy.

Methods

Western blot was applied to determine the expression of FEN1‐ and apoptosis‐related proteins. Cell growth inhibition assay and colony formation assay were used to determine the effects of FEN1 inhibitor and IR exposure for Hela cells in vitro. CRISPR technology was used to knockdown FEN1 expression level of 293T cells, and tumor xenograft in nude mice was employed to determine the effects of FEN1 inhibitor and IR exposure on tumor growth in vivo.

Results

Our data revealed that FEN1 is overexpressed in HeLa cell and can be upregulated further by IR. We also demonstrated that FEN1 inhibitor enhances IR sensitivity of cervical cancer in vitro and in vivo.

Conclusion

FEN1 inhibitor SC13 could sensitize radiotherapy of cervical cancer cell.

MicroRNA-140 impedes DNA repair by targeting FEN1 and enhances chemotherapeutic response in breast cancer

An increased DNA repair capacity is associated with drug resistance and limits the efficacy of chemotherapy in breast cancers. Flap endonuclease 1 (FEN1) participates in various DNA repair pathways and contributes to cancer progression and drug resistance in chemotherapy. Inhibition of FEN1 serves as a potent strategy for cancer therapy. Here, we demonstrate that microRNA-140 (miR-140) inhibits FEN1 expression via directly binding to its 3' untranslated region, leading to impaired DNA repair and repressed breast cancer progression. Overexpression of miR-140 sensitizes breast cancer cells to chemotherapeutic agents and overcomes drug resistance in breast cancer. Notably, ectopic expression of FEN1 abates the effects of miR-140 on DNA damage and the chemotherapy response in breast cancer cells. Furthermore, the transcription factor/repressor Ying Yang 1 (YY1) directly binds to the miR-140 promoter and activates miR-140 expression, which is attenuated in doxorubicin resistance. Our results demonstrate that miR-140 acts as a tumor suppressor in breast cancer by inhibiting FEN1 to repress DNA damage repair and reveal miR-140 to be a new anti-tumorigenesis factor for adjunctive breast cancer therapy. This novel mechanism will enhance the treatment effect of chemotherapy in breast cancer.

Next-generation paclitaxel-nanoparticle formulation for pancreatic cancer treatment

Pancreatic cancer (PanCa) is a major cause of cancer-related death due to limited therapeutic options. As pancreatic tumors are highly desmoplastic, they prevent appropriate uptake of therapeutic payloads. Thus, our objective is to develop a next-generation nanoparticle system for treating PanCa. We generated a multi-layered Pluronic F127 and polyvinyl alcohol stabilized and poly-L-lysine coated paclitaxel loaded poly(lactic-co-glycolic acid) nanoparticle formulation (PPNPs). This formulation exhibited optimal size (~160 nm) and negative Zeta potential (-6.02 mV), efficient lipid raft mediated internalization, pronounced inhibition in growth and metastasis in vitro, and in chemo-naïve and chemo-exposed orthotopic xenograft mouse models. Additionally, PPNPs altered nanomechanical properties of PanCa cells as suggested by the increased elastic modulus in nanoindentation analyses. Immunohistochemistry of orthotopic tumors demonstrated decreased expression of tumorigenic and metastasis associated proteins (ki67, vimentin and slug) in PPNPs treated mice. These results suggest that PPNPs represent a viable and robust platform for (PanCa).

Discovery of Myricetin as a Potent Inhibitor of Human Flap Endonuclease 1, Which Potentially Can Be Used as Sensitizing Agent against HT-29 Human Colon Cancer Cells

Human flap endonuclease 1 (hFEN1) is instrumental in DNA replication and repair. It is able to cleave the 5' single-stranded protrusion (also known as 5' flap) resulting from strand displacement reactions. In light of its crucial functions, hFEN1 is now deemed as a nontrivial target in the DNA damage response system for anticancer drug development. Herein, we report that myricetin and some natural flavonoids are able to inhibit hFEN1. Structure-activity relationship, inhibitory mechanisms, molecular docking, and cancer cell-based assays have been performed. Our original findings expand the activity of flavonoids and may pave the way for flavonoid-assisted targeted cancer therapy.

The resistance of esophageal cancer cells to paclitaxel can be reduced by the knockdown of long noncoding RNA DDX11-AS1 through TAF1/TOP2A inhibition

Esophageal cancer (EC) is one of the most common malignancies in the world. The currently used chemotherapeutic drug for the treatment of EC is paclitaxel (PTX), the efficacy of which is affected by the development of drug resistance. The present study aims to define the role of the long noncoding RNA (lncRNA) DDX11-AS1 in the progression of EC with the involvement of PTX-resistant EC cells. First, EC and adjacent normal tissue samples were collected from 82 patients with EC, after which the expression levels of DDX11-AS1, TOP2A and TAF1 were determined. The results showed that DDX11-AS1, TOP2A and TAF1 were highly expressed in EC tissues, and there was a positive correlation between the expression levels of DDX11-AS1 and TOP2A. A PTX-resistant EC cell line was constructed. Next, we evaluated the effects of DDX11-AS1 and TOP2A on the resistance of EC cells to PTX, and the regulatory relationships between DDX11-AS1, TOP2A and TAF1 were investigated. DDX11-AS1 could promote TOP2A transcription via TAF1, and the knockdown of TOP2A or DDX11-AS1 could increase the sensitivity of EC cells to PTX. The effect of DDX11-AS1 on the growth of PTX-inhibited tumors was confirmed using a tumor formation assay in nude mice. It was verified that knocking down DDX11-AS1 reduced the expression level of TOP2A and inhibited tumor growth. In conclusion, our findings suggest that DDX11-AS1 knockdown results in reduced resistance of EC cells to PTX by inhibiting TOP2A transcription via TAF1. Therefore, DDX11-AS1 knockdown could be a promising therapeutic strategy for EC.

Pharmacological and polyphenolic profiles of Phyllanthus phillyreifolius var. commersonii Müll. Arg: An unexplored endemic species from Mauritius

Phyllanthus phillyreifolius var. commersonii Müll. Arg is an endemic plant of Mauritius. To date, no study has been performed concerning its polyphenolic profile and pharmacological properties. In this study, a decoction (water), ethyl acetate and methanol extracts of the aerial parts of P. phillyreifolius, obtained from different extraction procedures (maceration and Soxhlet), were studied for antibacterial, antioxidant, anticancer, and enzyme inhibitory properties along with their polyphenolic profile. The ethyl acetate macerated extract showed high antibacterial activity against B. cereus (MIC = 0.293 mg/mL) and E. coli (MIC = 0.417 mg/mL) while S. epidermidis was most susceptible to the ethyl acetate-Soxhlet extract (MIC = 0.521 mg/mL). The methanol-Soxhlet extract displayed the most potent cupric and ferric reducing power, and metal chelating effect, while the macerated methanolic extract was the most effective DPPH and ABTS scavenger, and BChE inhibitor. Only the ethyl acetate-Soxhlet extract exhibited α-glucosidase inhibition. All extracts exhibited a strong anti-tyrosinase activity, which was further investigated by molecular docking and molecular dynamic. After 48 h exposure to the extracts for HeLa cell lines, the ethyl acetate-Soxhlet extract showed the highest inhibition (IC₅₀ = 533.1 μg/mL) while the decoction extract was more cytotoxic to MDA-MB-231 cells (IC₅₀ = 337.4 μg/mL). Treatment of cancer cell lines with all P. phillyreifolius extracts resulted in a time-dependent reduction of cell viability for HeLa and dose-and time-dependent reduction for MDA-MB-231. Gene expression ratio of Bcl-2 to Bax was higher for all Soxhlet-extracts. Total phenolics (TPC) and flavonoids (TFC) content were highest in the decoction and methanol-Soxhlet extract, respectively (122.43 mg GAE/g extract and 31.28 mg RE/g extract, respectively). The extracts were abundant in ellagitannins, although phenolic acids and flavonoids were also detected. Granatin B was detected for the first time in Phyllanthus species. Overall, the aerial parts of P. phillyreifolius exemplify a potent reservoir of bioactive phytochemicals for therapeutic applications.